1. Field of the Invention
The present invention is broadly concerned with compositions of two or more peptides effective in inhibiting the binding of proteins, and corresponding methods of use. More particularly, the preferred form of the invention relates to peptide compositions which inhibit the binding of leukocyte function-associated antigen (LFA-1) and intercellular adhesion molecule (ICAM-1); these peptide compositions can be used to treat disease states such as rejection of transplanted organs, allergies, and autoimmune diseases.
2. Description of the Prior Art
Many biological phenomena involve the mutual recognition of proteins. For example, it has been known for decades that antibodies bind to antigens in order to protect the body against foreign substances (Carayannopoulos et al., 1993, Immunoglobulins, Structure and Function, In: Fundamental Immunology, Paul, W. E., Ed., pp. 283-314, Raven Press). Also, Ras and Raf-1 are proto-oncoproteins that transduce growth and differentiation signals initiated by tyrosine kinases; ras binds to Raf-1 and thereby inhibits Ras-GAP activity (Zhang et al., 1993, Nature 364:308-313). Yeast Cdc7 protein kinase and Dbf protein are both required for the initiation of DNA replication; these proteins bind to each other, and it is thought that Dbf4 is specific for the activation of Cdc7 kinase (Jackson et al., 1993, Mol. Cell Biol. 13:2899-2908). Yeast GAL4 protein consists of two protein subunits which, when bound together, activate the genes encoding enzymes of galactose utilization (Fields et al., 1989, Nature 340:245-246).
It is also widely known that the contact sites within proteins that bind to one another are noncontinuous domains of amino acids. These contact sites can be found in different subunits of a protein as in the case of the heavy and light chains of antibodies (Carayannopoulos et al., 1993; Perutz, 1992, Protein Structure, New Approaches to Disease and Therapy, pp. 41-76, W. H. Freeman and Co.). Alternatively, these contact sites can be found in different areas of the same subunit as in the case of the .alpha. subunit of LFA-1 (Edwards et al., 1995, J. Biol. Chem. 270:12635-12640; Stanley et al., 1994, EMBO 13:1790-1798).
Many autoimmune diseases occur when T-cells of an organism recognize and react to "self" proteins. This recognition occurs when specific proteins on the surface of the T-cells bind to the corresponding self proteins. This type of reaction results in rheumatoid arthritis, insulin-dependent diabetes mellitus, and multiple sclerosis. Allograft rejection also results from T-cell attack.
Initiation of an immune response to an antigen involves interaction of a small subset of T-cells with the antigen, followed by activation and proliferation of those T-cell clones. Complete T-cell activation requires two signals: (1) interaction of the T-cell receptor with an appropriate MHC-antigen complex, and (2) a second signal provided by adhesion molecules. The second signal may be provided by binding of the adhesion receptor, LFA-1 (CD11a and CD18), to one of its counter-receptors such as ICAM-1 (CD54) (Staunton et al., 1990, Cell 61:243-254). If the second signal is blocked, the antigen-specific T-cells are induced to die by apoptosis or to enter a state of cellular anergy. Blockage of this interaction by monoclonal antibodies to LFA-1 and ICAM-1 results in increased survival time for mice receiving heart allografts (Isobe et al., 1992, Science 255:1125-1127).
Previous studies have shown that peptide fragments from ICAM-1 can inhibit T-cell-endothelial adherence (Ross et al., 1992, J. Biol. Chem. 267:8537-8543), HIV-1 replication in MT-2 cells (Fecondo et al., 1993 Aids Research and Human Retroviruses 9:733-740), homotypic adhesion of Raji cells, and cytotoxic cell-mediated killing of K562 cells. Peptides from the sequence of the .alpha. subunit of LFA-1 have also been shown to inhibit binding of T-cells to ICAM-1 (Stanley et al., 1994, EMBO 13:1790-1798). Additionally, short-chain peptides derived from active sites of ICAM-1 and LFA-1 also inhibit these types of interactions (Benedict et al., 1995, International Publication No. WO 95/28170, the teachings of which are incorporated by reference herein). However, there are no reports in the prior art of peptide compositions which are effective in inducing immune tolerance in an organism.